This invention relates to water-repellant yarns, to a process for making such yarns, and to fabrics produced from them.
It is well known that for a variety of purposes, water repellant fabrics are highly desirable. Typical applications are tarpaulins, tents, and various items of clothing. The level of water repellency, often erroneously also called water proofing (true water proofing can only be obtained with a continuous, water impermeable membrane) desired depends upon the end-use contemplated, and can vary from "shower proofing" (so-called) upwards. The known water repellent fabrics are generally prepared by treating the fabric -- which may be woven, knitted, or non-woven such as felt -- either before or after it has been made into the marketed product, with a water repelling agent, whereby a coating is left on the fabric. Usually this process is applied to the fabric as the last stage in its manufacture, prior to its being made up into a saleable article.
These known processes whereby water repellent coatings are applied to a fabric generally involve three steps, which are applied to a continuous single layer of fabric as it passes through a suitable treatment machine; for example by unrolling it from a bolt of cloth: first, a solution or dispersion of the agent is applied to the fabric; second, excess solvent is removed; and third, the fabric is briefly heated in order to cure the water repellent onto the fabric.
This procedure suffers from at least two major disadvantages. First, the treatment plant has to be wide enough to handle in flat form the fabric being processed. Since modern looms can produce fabrics up to at least 15 feet wide, this makes the treatment plant extremely expensive. Second, it is now common practice to produce fabrics from a mixture of yarns: but if a fabric is to be rendered water repellent, only yarns that will not be adversely affected by the treatment process may be used.
We have also found that nearly all the available processes for rendering a fabric water repellent cannot be applied to a yarn by means of conventional dye-house equipment, particularly a yarn including a synthetic fibre, in bulk or package form. By `bulk or package form` is meant an amount of yarn as a thick skein, or wound onto a bobbin or the like. All of the known systems involve applying heat to the treated material in order to cure the repellent onto the fibre. We have found that with these known processes intended for fabrics, in order to obtain the required temperature at the center of a mass of yarn on a bobbin it is necessary to use such a high temperature that the yarn on the outside of the bobbin is adversely affected.